import { prop } from 'tfrp';
import { on } from 'remini';

class Todos {
  @prop items = [];

  constructor() {
    on(() => this.items, () => console.log('items changed'));
  }

  add(todo: string) {
    this.items = this.items.concat(todo); // an immutable modification
  }
}

import { prop, cache } from 'tfrp';

class Todos {
  @prop items = [];

  @cache get completed() {
    return this.items.filter(item => item.completed);
  }
}